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© 2005 Plant Management Network.
Accepted for publication 1 April 2005. Published 6 May 2005.

Strip Cutting Alfalfa for Lygus Management: Forage Quality Implications

Shannon C. Mueller, Agronomy Farm Advisor, University of California Cooperative Extension, 1720 S. Maple Avenue, Fresno 93702; Charles G. Summers, Entomologist, Department of Entomology, University of California, Davis 95616, and Kearney Agricultural Center, University of California, 9240 S. Riverbend Ave., Parlier 93648; and Peter B. Goodell, Area IPM Advisor, Statewide IPM Program, Kearney Agricultural Center, University of California, 9240 S. Riverbend Ave., Parlier 93648

Corresponding author: Shannon C. Mueller. scmueller@ucdavis.edu

Mueller, S. C., Summers, C. G., Goodell, P. B. 2005. Strip cutting alfalfa for lygus management: Forage quality implications. Online. Crop Management doi:10.1094/CM-2005-0506-01-RS.

Abstract

Strip cutting is used to limit lygus migration from forage alfalfa into susceptible neighboring crops when the alfalfa is harvested. Hay growers are concerned that uncut strips remaining from the previous harvest may negatively affect the quality and marketability of alfalfa forage during subsequent cuttings. The objective of this trial was to determine if blending old alfalfa growth from uncut strips with new growth alfalfa could mitigate reductions in quality. Based on individual cuttings, blends of 75/25 new/old alfalfa had only a minimal impact on hay quality compared to 100% new growth alfalfa and in most cases quality did not differ from that of 100% new alfalfa. Crude protein (CP) was not affected in three of six cuttings over two years and in those where crude protein values were reduced, the reduction was likely caused by leafhopper (Empoasca spp.) feeding or by excessively high temperatures and water stress. Acid Detergent Fiber (ADF), used to calculate several quality parameters, was not impacted by blends that included 25% old alfalfa in four of six cuttings over two years. While blends of 75/25 new/old alfalfa and 50/50 new/old alfalfa may not qualify as prime feed for lactating dairy cows, such blends are acceptable for use as horse hay, and for beef and dry cow hay.

Introduction

Strip cutting was originally developed as a management tool to reduce the migration of lygus bugs from forage alfalfa, Medicago sativa L., into cotton, Gossypium hirsutum (L.) (17,22). It consisted of harvesting alternate strips (250 to 300 ft wide) of alfalfa at two-week intervals throughout the summer to assure that some lush alfalfa was always available to attract and hold lygus bugs. While this system worked well as an insect management strategy, it created operational constraints that proved to be obstacles to its adoption, since the strips had to be managed as separate fields within a field thus complicating irrigation and harvesting operations.

Summers (18) proposed an alternative strategy called border cutting. Here, narrow (10-ft) strips of uncut alfalfa were left on alternate irrigation borders as an insect refuge. At the following harvest, these strips ("old hay") were cut, and new uncut strips were left as a refuge on alternate levees. The old hay was blended with new growth alfalfa during swathing and raking to minimize reductions in forage quality. This approach worked well in reducing insect emigration and avoided the operational problems associated with strip cutting. However, there were concerns about the nutritional quality of the blended bales, so border cutting was not readily adopted. In the mid 1990s, problems with lygus bug control, insecticide resistance, and environmental concerns about pesticide use rekindled interest in border cutting (6). In a 2000 survey of California IPM practices in cotton (P. B. Goodell, S. B. Brodt, and R. L. Krebill-Prather, unpublished), 41% of the respondents reported using border cutting or block cutting in alfalfa to preserve alternate lygus habitat. However, there continue to be concerns regarding forage quality with blended ("old" and "new") alfalfa in the same bale. These concerns currently limit the implementation of this alternative pest management practice, particularly in alfalfa destined for the dairy market. The objective of this study was to determine how best to blend old and new growth alfalfa to mitigate quality reductions when strips of uncut alfalfa are used for insect management.

Field Design and Blending Procedure

Three cuttings were selected for blending of old and new alfalfa: late June, mid August, and mid September (2000); and early June, early July, and late August (2001). The time of cutting in the two years differed slightly due to the timing of the first cutting, which may vary by two to three weeks depending on spring weather conditions. The cutting made prior to the June harvest in each year was a strip cutting so old alfalfa would be available for blending in the next cutting. Three five-acre alfalfa fields at the UC Kearney Research and Extension Center in Parlier, CA were used in the study. Each field was considered a block (replication) and the treatments (bale compositions) were randomly assigned within each of the five acre fields resulting in a randomized complete block design with three replications (fields) and four treatments (blends). Blending of old and new alfalfa was done on the basis of area. Bales containing different proportions of old and new growth were created by swathing proportionate widths of old and new alfalfa and blending, by raking, the respective windrows together (Fig. 1). All blends were created using standard 14-ft (cutter bar) field harvesting equipment to insure that growers and custom harvesters could duplicate the technique. In 2000 and 2001, 14-ft-wide strips were left uncut at 84-ft intervals across the field. At the next cutting, when the swather cut the entire old strip (14 ft wide) and it was maintained as a single windrow, bales from that windrow contained 100% old hay. Likewise, if a previously uncut strip ("old hay") was completely avoided during the next regularly scheduled cutting, the bales contained 100% new hay. To create the 50/50 blend, the swather divided the previously uncut strip ("old hay") in half (seven feet) and also cut seven feet of new hay. The two adjacent windrows each contained 50% old and 50% new hay. To create bales composed of 25% old and 75% new hay, the 14-ft strip of old growth was split in half (seven feet) by the swather plus seven feet of new hay as in the previous example. The two adjacent windrows were a 50/50 blend of old and new growth. Each of them were then raked with an adjacent windrow of 100% new growth and baled creating a final composition of 25% old and 75% new hay.

Fig. 1. Swathing and raking procedure used to create bales of various composition during 2000 and 2001.

Chemical and Visual Analysis

Bales were sampled using a Penn State Forage Sampler (Nasco West, Modesto, CA) (2). Each sample was analyzed (Manna Pro Labs, Fresno, CA) for crude protein (CP) and acid detergent fiber (ADF). Subjective evaluation of forage quality factors (i.e., leafiness, color, aroma, and overall quality) were performed by an experienced, independent hay broker. Forage quality factors were rated by blind evaluation on a one to three scale with one = best and three = worst.

Statistical Analysis

Since alfalfa is generally bought and sold by individual cutting, we chose to analyze each cutting separately, rather than to evaluate the interactions between quality and harvest date that, while interesting, do not play a role in marketing. Data for each individual cutting were evaluated by an appropriate ANOVA procedure, and means were separated using Fisher's Protected LSD (15). Treatment differences where P ≤ 0.05 were considered significant.

Forage Quality: Chemical Analysis

Dry matter. Dry matter is defined as the percentage of forage that is not water (7). Extremely low moisture content at baling (< 10%) can result in brittleness and excessive leaf loss from shatter, while excessive moisture (> 22%) may lead to the development of mold or heat buildup within the bale (3). There were no significant effects of bale composition on dry matter content in any year (data not shown). Forage moisture percentages were acceptable, ranging between nine and 12% (3). Moisture content of the bale declines slightly following baling (2).

Crude protein. Crude protein (CP) is calculated from the nitrogen content of the forage, which is present primarily in the leaf fraction. Spring and fall cuttings typically have higher proportions of leaves than do summer-cuttings (2). The leaf biomass, hence CP, in forages can also be reduced by growth stage at cutting, by insects, foliar disease, drought, and high temperatures (4,5,19,20,21,23). The crude protein content of the 75/25 new/old blends did not differ from the 100% new hay in June 2000, but was significantly lower in both August and September (Table 1). The fields experienced a severe leafhopper (Empoasca spp.) infestation in August and September, 2000 (Fig. 2). While lower quality was expected in August, the lower crude protein in September may have resulted from extensive leafhopper feeding (4,9). Protein losses are especially severe as alfalfa nears maturity (16). The difference in CP between 100% new hay and the 75/25 blend was 2% in June, 11% in August and 12% in September. The continuing leafhopper pressure on the "old" hay that went into the 75/25 blend in both months could account for the reduced protein content. Except for the first (June) cutting, the 50/50 blend of old and new hay was significantly lower in CP than either the new hay or the 75/25 blend and did not differ significantly from the 100% old hay in all three cuttings (Table 1).

Fig. 2. Uncut strip of alfalfa ("old hay") showing severe Empoasca leafhopper injury. Note also the increasing injury in the form of yellowing adjacent to the uncut strip reflecting the movement of leafhoppers out of the strip into the surrounding alfalfa.

In 2001, CP in the 75/25 new/old blend was significantly lower than the 100% new hay in the June cutting, but not significantly lower in the other two cuttings (Table 2). Weather conditions preceding the June cutting were extreme, with average May temperatures (max/min) 11°F above normal with 10 days exceeding 100°F (14). In addition, problems with irrigation resulted in severely stressed alfalfa prior to the June cutting, resulting in poor leaf quality and increased fiber content. Crude protein in the 50/50 blend did not differ significantly from the 100% old hay in the June cutting, but did differ in the July and August cuttings.

Table 1. Crude protein and acid detergent fiber values (± SEM) from selected blends of old and new growth alfalfa on three cutting dates in 2000.

 ^† Crude protein and acid detergent fiber values are reported at 100% dry matter.

 * Means within each column followed by the same letter(s) are not significantly different at P = 0.05. Fishers protected LSD.

** Significant at P ≤ 0.01.

Table 2. Crude protein and acid detergent fiber values (± SEM) from selected blends of old and new growth alfalfa on three cutting dates in 2001.

 ^† Crude protein and acid detergent fiber values are reported at 100% dry matter.

 ^‡ Means within each column followed by the same letter(s) are not significantly different at P = 0.05. Fishers protected LSD.

 * Significant at P ≤ 0.05.

** Significant at P ≤ 0.01.

Acid detergent fiber. Acid Detergent Fiber (ADF) consists primarily of cellulose and lignin, with some insoluble protein and insoluble minerals such as ash (2). As alfalfa matures and the stems become more lignified, ADF values increase. Alfalfa quality associated with advancing maturity is strongly influenced by temperature (i.e., increased temperatures generally mean increased ADF values), and is greater in the summer than the spring or fall (11,12). ADF has a strong negative correlation with total forage digestibility and as ADF increases, forage quality declines (2). The constituents of ADF are the least digestible portions of the plant material; therefore, the higher the ADF, the less digestible the forage (2). Acid Detergent Fiber values were not significantly different in any year for the 75/25 new/old blend compared to 100% new hay, except June and July of 2001. The excessively high temperatures preceding the June cutting, as noted above, likely contributed to the increase in ADF value. In the majority of cases, there was little or no difference between the 75/25 new/old blend and 100% new alfalfa. Where differences existed, environmental conditions, excessively high temperatures, and/or water stress were the likely causal factors. The 100% old hay was uniformly higher in ADF than the 100% new hay.

Forage Quality: Subjective Inspection

Both visual inspection and laboratory analysis predict the quality and potential feeding value of alfalfa hay. These techniques are best used in combination because there are certain characteristics that cannot be evaluated by standard chemical analysis, such as the presence of weeds, objectionable odors, dust, or mold that decrease palatability (2).

Leafiness. Leafiness was evaluated on a scale from one to three, with one indicating leafy hay and three indicating stemmy hay. There were no significant differences in leafiness due to bale composition in either year (Tables 3 and 4).

Table 3. The influence of blends of new and old alfalfa on selected quality parameters (± SEM) as determined by visual inspection* in 2000.

 * Ratings were generated using blind evaluation by an experienced hay broker (1-3, 1 = best, 3 = worst).

 ^† Means within each column followed by the same letter(s) are not significantly different at P ≥ 0.05. Fishers Protected LSD. ns = Not significant, ** Significant at P ≤ 0.01.

 ^‡ In 2000, the evaluations for color and aroma were combined.

Table 4. The influence of blends of new and old alfalfa on selected quality parameters (± SEM) as determined by visual inspection* in 2001.

 * Ratings were generated using blind evaluation by an experienced hay broker (1-3, 1 = best, 3 = worst).

 ^† Means within each column followed by the same letter(s) are not significantly different at P ≥ 0.05. Fishers Protected LSD. ns = Not significant.

 ^‡ In 2001, the evaluations for color and aroma were conducted separately.

Color and aroma. Color and odor are important characteristics because they indicate how well the hay was cured in the field and preserved in the bale. Evaluation of color and aroma is part of the standard visual evaluation and is especially important for hay destined for the horse market. Buyers generally purchase horse hay based on leafiness, color, aroma (lack of a moldy smell), and lack of dust (John Diamond, hay broker, personal communication). Older growth, particularly in mid-summer, is courser and dries more slowly. It could have a tendency to form wet slugs in the bale leading to heating or moldy conditions. In 2000, color and aroma were evaluated together, while in 2001, they were evaluated separately. No sour or moldy odor was found in any of the harvest dates over the two-year study, although in June of 2000, the blends of 50/50 new/old and 100% old hay were significantly poorer in color and aroma than were the 75/25 blend or 100% new hay (Tables 3 and 4). Such hay would likely be rejected by an astute buyer of both dairy and horse hay (13) without even looking at the chemical analysis. Such hay might be acceptable to the beef producer. The 75/25 new/old hay showed no significant difference in color or aroma compared to the 100% new hay.

Overall quality. Overall quality combines a number of factors, some discussed above and others, such as rain damage, weed, dust, and foreign matter content (data not shown) which were not significantly different for any of the blends in any year. The overall quality rating was the "bottom line" rating by an experienced hay broker as to the marketability of the hay. Overall quality was not significantly different in any of the blends except the June harvest in 2000 (Tables 3 and 4). In this particular harvest, the 50/50 blend was significantly lower in overall quality than the 100% new hay or the 75/25 new/old blend. It did not differ from the 100% old hay. Based on visual evaluation, the buyer would not reject the 75/25 new/old blend, but might reject the 50/50 blend depending on the end-use of the hay.

Summary

Our studies show that during the time period June through September, when it is useful to manipulate insect migration by leaving unharvested strips of alfalfa in the field, new and old alfalfa can be successfully blended to maintain acceptable forage quality. Caution should be used to make sure that such blends do not contain more than 25% old alfalfa blended with 75% new alfalfa. Prime dairy hay, fed to lactating cows, should be 20% + CP and < 30 to 31% ADF (1,2). The 75/25 blend may not always meet these criteria. Other livestock, however, can have their nutrient needs met with lower quality forage (6,9). Even the 50/50 blend, based both on chemical and visual analysis, may be acceptable to certain buyers depending on the final disposition of the hay. For example, buyers of horse hay tend to use visual inspection to a high degree in selecting forages, looking primarily at leafiness, color, and aroma. These characteristics are most often associated with early maturity alfalfa. In many cases, however, mid-to-late maturity alfalfa is a more appropriate feed. Non-working horses have relatively low nutrient requirements and can meet most, if not all of their nutrient needs with lower quality hay (13). Feeding high quality hay to such animals will satisfy their nutrient needs, but not necessarily their chewing needs which may be redirected to fences, stalls, or trees (13). Feeding the lower quality hay can satisfy both. Hay with a CP of 12 to 14% and an ADF of 41 to 42% is generally acceptable for beef and dry dairy cows (7,10). Heifers, three to 12 months old do well on 16 to 18% CP and 33 to 38% ADF (8). Both the 75/25 and the 50/50 blends meet these criteria.

In none of the six cuttings evaluated over two years did CP in either the 50/50 blend or the 100% old hay attain the level of the 100% new hay. The 50/50 blends faired slightly better with regards to ADF. In the late summer/early fall cutting in each year, ADF in the 50/50 blends were not statistically higher that those in the 100% new hay. Blends containing > 50% old hay are unsatisfactory as dairy cow feed and should not be used by growers expecting to market the hay for that purpose. As noted above, they will fit into a ration mix for beef cattle and dry cow hay.

Conclusions

These findings provide support in encouraging farmers to preserve lygus habitat through strip cutting during critical periods when cotton or other susceptible crops are likely to be injured and require insecticide treatments for lygus control. Hay from the blends, while not appropriate as feed for lactating dairy cows, is suitable for horses and for mixing in rations for beef and dry cows. This may require a bit more aggressive approach on the part of the grower to develop these additional markets, but would be well worth it in terms of cost savings relative to insecticide use in susceptible crops grown adjacent to alfalfa. An added benefit of strip cutting alfalfa is the retention of natural enemies in the alfalfa field itself, thus reducing the need for insecticides in that crop (18). Growers who plan to strip cut and blend old and new alfalfa should pay particular attention to factors that could additionally affect quality such as insect infestations, weather conditions, and irrigation.

Acknowledgments

We thank Albert Newton, Ryan Smith, Chuck Haas, and Cecelia Garcia for technical assistance with this project. We are particularly grateful to Dan Mulligan for his incredible patience in dealing with the swathing, raking, and baling required to create the various blends. We are grateful to Dan Putnam and Peter Robinson for their critical review of an earlier draft of the manuscript, which improved it measurably. Portions of this research were funded by a grant from the California Department of Pesticide Regulation.

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